Note: Descriptions are shown in the official language in which they were submitted.
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MASS TERMINABLE FLAT CABLE ASSEMBLY WITH
READILY SEPARABLE GROUND PLANE _
The present invention relates to electrical
wiring components and, more specifically, to a flat
cable assembly having an integral ground plane, for use
with mass termination, insulation displacement
connectors.
Backqround of the Invention
Mass termination, insulation displacement
connectors have come into increasing commercial
prominence because of the significant savings in time
and labor they offer compared to stripping and
individually terminating each conductor using a crimp
terminal. These connectors have an insulative body
holding a number of regularly spaced terminal elements
having slotted plates terminating in sharpened free ends
extending beyond a surface of the body. The conductors
also include covers having recesses in a facing surface
for receiving the free ends of the plates. After the
insulated conductors are aligned with their
~ corresponding slotted plates, relative closing of the
; body and cover results in displacement of the insulation
with the conductors contacting the metallic plates. For
further information regarding the operation and
structure of such connectors, reference may be made to
U.S. Patent Nos. 4,458,967 and 3,912,354.
The most efficient form of conductors for use
; with such connectors is the flat cable in which
conductors, running parallel and spaced to match the
spacing of the terminal elements in the connector, are
held by a layer of insulation. The use of a flat cable
avoids running the conductors one at a time and holding
them in position for termination. The flat cable-can be
used for either a daisy chain connection (where the
connector is applied intermediate the cable ends) or an
end connection. The sharpened ends of the slotted
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plates pierce the web material between the conductors in
the flat cable as the body and cover close so slitting
of the cable between conductors is not required.
In certain applications, it is advantageous to
incorporate in the flat cable a metallic ground plane
having a width such that it extends beyond the discrete
conductors. But for the presence of the ground plane,
the impedance and capacitance of the flat cable could
vary in accordance with its proximity to metallic
structure. The use of a ground plane stabilizes and
reduces impedance and, furthermore, functions to reduce
crosstalk among the various conductors, which crosstalk
could adversely affect the operation of computers and
peripheral equipment. Heretofore, the ground plane
typically was embedded in the layer of insulation along
with the conductors. Special powered tools were
required to cut the insulation to permit access to the
ground plane so that it could be peeled away from the
conductors to prepare for their mass termination. If
the removal of the ground plane was done improperly, the
electrical and dimensional characteristics of the cable
could be adversely affected.
It is known to releasably connect a stack of
flat cables with a perforated separator strip disposed
between each pair of cables. By the application of heat
and pressure, the cables bond at the perforations. ~he
limited adhesion holds the cables joined until manual
separation is desired. For further information
regarding the operation and structure of such cables,
reference may be made to U.S. Patent No. 3,173,991.
It is also known to provide a tape conductor
including a conductive strip sandwiched between a base
layer having an adhesive coating facing away from the
strip, and a cover layer with an adhesive coating for
securing the tape to the base layer. By selective
arrangement of adhesive patches, the peel force required
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to remove the cover layer can be varied. For further
information concerning such a tape conductor, reference
may be made to U.S. Patent No. 2,964,587.
Summarv of the Invention
Among the various aspects and objects of the
present invention may be noted the provision of an
$mproved flat cable assembly incorporating a ground
plane. ~he flat cable assembly includes a cover for the
ground plane which can be manually removed, without the
use of special tools, to expose the ground plane and
permit its deflection from the main cable, to prepare
the main cable for mass termination. The flat cable
assembly of the present invention has substantially the
same thickness as prior flat cables including integral
ground planes and also has substantially the same weight
per unit length. The flat cable assembly is reliable in
use, has long service life and is easy and economical to
manufacture. Other aspects and features of the present
invention will be, in part, apparent and, in part,
pointed out specifically hereinafter in the following
specification and the attached claims and drawings.
Briefly, the flat cable assembly of the present
invention includes a main flat cable having a plurality
of conductors held in regularly spaced, parallel
relationship in a sheet of insulation to match the
terminal element spacing of the mass termination
connector. The main cable has a first surface, a second
surface, and lateral edges with the surfaces extending
between the lateral ends. A plastic covering has an
interior surface facing the cable second surface with a
release agent printed in a pattern on the interior
surface so that portions of the interior surface are
coated by the release agent and other portions of the
interior surface are uncoated. The cable assembly also
includes a metallic ground plane positioned between the
main cable and the covering, with the covering being
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bonded to the second cable surface at uncoated portions
of the interior surface so the plastic covering can be
readily removed to expose the ground plane.
Brief Descri~tion of the Drawinqs
FIG. 1 illustrates a flat cable assembly
embodying various features of the present invention with
the various components of the assembly separated;
FIG. 2 is a cross-sectional view of the cable
of FIG. 1; and
FIG. 3 is an exploded perspective view showing
a mass termination, insulation displacement connector
usable with the cable assembly of FIG. 1.
Corresponding reference numbers indicate
corresponding components throughout the several views of
the drawings.
DescriPtion of the Preferred Embodiment
Referring now the drawings, a flat cable
assembly of the present invention adapted for use with a
mass termination, insulation displacement connector 22
~shown in FIG. 3), is generally indicated by reference
numeral 20. The flat cable assembly 20 is of laminated
construction and includes a main cable 24 including a
plurality of conductors i6 held in regularly spaced,
parallel relationship in a layer of insulation 28. The
cable assembly 20 includes a plastic covering 29 with a
ground plane conductor 30 sandwiched between the main
cable and the plastic covering. A drain wire 31, in
intimate contact with the ground plane 30, may also be
included in the cable assembly. While the particular
flat cable illustrated is intended for carrying
electrical signals and has the conductors on .050 inch
centers, it will be appreciated that the flat cable 20
of the present invention can be made in larger sizes for
use in supplying electrical power to various electrical
components.
The mass termination connector 22 shown in
FIG. 3 is of the high terminal density, signal conductor
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type and includes an insulative body 32 having two rows
of terminal element cavities. A terminal element 33 is
disposed in each cavity with elements in each row having
a .100 inch pitch. Adjacent terminal elements in each
row are staggered so that every other conductor 26 is
terminated by elements in one row while the remaining
conductors are terminated by the elements in the other
row. Each terminal element includes a slotted plate 34
extending beyond a surface 36 of the body with the plate
terminating in sharpened ends for piercing the web
material of the flat cable between the conductors. The
plate edges defining the slot function to displace the
insulation material so that by forcing a conductor 26
into a slotted plate 34, the conductor is engaged by the
metallic plate to establish an electrical circuit. The
connector 22 also includes a cover 37 held in alignment
with the body 32 by means of pins 38. The cover, also
formed of insulating material, includes a facing
surface 40 having pockets 42 for locating tne flat cable
- 20 conductors 26 with respect to the terminal elements 33,
and a recess 44 for receiving the free ends of the
slotted plates 34. Thus, after the flat cable 20 is
positioned between the cover 37 and the body 32,
relative closing of the two results in mass termination
of the conductors 26 of the flat cable 20.
Referring to FIGURES 1 and 2, the main cable 24
has a first surface 46 and a second surface 48 and
lateral ends 50 with the first and second surfaces
extending between the lateral ends; The plastic
covering 29 has an interior surface 52, facing the cable
- second surface, which has a release agent 54 printed
thereon so that portions of the interior surface are
coated by the release agent and other portions of the
interior surface remain uncoated. It will be
appreciated that the release agent could be instead
printed on the main cable second surface 48, or on both
surface 52 and on surface 48. The release agent is
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shown as having been applied in a dot matrix foem with
the dots representing uncoated or bondable areas on the
interior surface of the plastic coating. The
application of heat and pressure will cause the plastic
covering to become adhered to the main cable second
surface 48 at the uncoated areas. About 70~ of the
total surface area on the interior surface 52 is coated
and there will be no bonding at these coated areas.
Thus, the force required to peel away the plastic
covering to expose the ground plane can be varied in
accordance with the coverage of the release agent.
Preferably the release agent takes the form of printing
ink of the type usable on plastic such as polyvinyl
chloride, which is the preferred material for the
insulation layer 28 as well as the plastic covering 29.
While the release agent is shown as being applied in a
dot matrix form, other arrangements of the printing
would also be acceptable, for example, adjacent
longitudinal or transverse strips of coated and uncoated
portions. The great advantage of the use of the printed
release agent is that the thickness and weight of the
total flat cable assembly is not increased in any
substantial way and the plastic covering can be peeled
away to expose the metallic ground plane 30 without the
use of any tools. Thus, preparation for termination of
the flat cable assembly 20 is much simpler than with
previous flat cables having integral ground planes
wherein the ground plane was embedded in a layer of
insulation along with tbe parallel conductors.
The first surface 46 of the main cable 24 is
preferably undulating, having a plurality of spaced
ridges 56 with one of the conductors 26 held in
alignment with each ridge. The ridges 56 are received
;~ by the pockets 42 in the connector cover 37 to properly
locate the various conductors 26 in alignment with their
corresponding slotted plates 34. This is advantageous
'~ over a flat cable having flat sides because the
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connector does not have to be provided with alignment
stops at the sides of the cover and/or body to position
the flat cable in position for termination.
~he second side 48 of the main cable preferably
5 has a centrally located depression 58 in which the
ground plane conductor 30, which is preferably of copper
mesh construction, is nested. As the ground plane
conductor 30 extends short of the lateral ends 50 of the
main cable 24, the ground plane is protected, ~oth
10 mechanically and electrically, from inadvertant contact
with metal structure. The uncoated portions of the
interior surface 52 of the plastic covering 29 are
bonded to the lateral portions of the main cable second
surface 48 flanking the ground plane. The second
15 surface 48 has a longitudinal groove 60 for seating the
drain wire 31 so that it is held in intimate contact
with the ground plane conductor 30 throughout the
longitudinal extent of the flat cable assembly 20.
Operation of the flat cable assembly 20 of the
20 present invention is as follows: In preparation for
termination of the main cable 24, the plastic
covering 29 is peeled away, either by hand or by the use
of very simple tools. This predetermined, limited
~dhesion of the plastic covering to the main cable
25 second surface 48 through the interstices of the copper
mesh ground plane 30 and to the lateral portions of the
second surface 48 of the main cable avoids the use of
power tools which could exhibit sufficiently large
forces to alter the dimensional and/or electrical
30 characteristics of the cable.
As shown in FIGURE 3, the ground plane
conductor 30 is also peeled back away from the main
cable. This is easily done because the ground plane 30
is a good conductor of heat. Thus, the heat and
35 pressure applied in the fusion of the plastic covering
to the main cable second surface 48 will not result in
any substantial adhesion of the ground plane conductor
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30 to the second surface 48. The insulation
displacement mass termination connector 32 can then be
closed about the main cable effecting termination of the
various conductors 26 in their corresponding slotted
; 5 plates 34. The ground plane conductor can then be
connected to ground in a conventional manner or cut away.
In view of the above, it will be seen that the
several objects of the invention are achieved and other
advantageous results attained.
As various changes could be made in the above
invention, it is intended that all matter contained in
the above description or shown in the accompanying
drawings shall be interpreted as illustrative and not in
a limiting sense.
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